The present application claims the priority of Japanese Patent Application No. 2000-233593, filed in Japan on Aug. 1, 2000, the entire contents of which is hereby incorporated herein by reference.
1. Field of Industry to Which the Invention Belongs
The present invention pertains to a substrate processing device and processing method and, in particular, it relates to a substrate-processing device in which a film is grown on a substrate while a magnetic field is imparted in a prescribed direction of the substrate.
2. Discussion of Related Art
In recent years, in the field of semiconductors and magnetic films, magnetic heads and recording elements have been proposed which employ a GMR (Giant Magnetoresistive structure) or a TMR (Tunnel Magnetoresistive structure) which generate an MR (Magnetoresistive effect) in which the electric resistance value is significantly altered by an external magnetic field (RandD Research and Development, July 1999, Vol. 41 No. 8 p 14-16).
A brief description of the MR effect will be given with reference to FIG. 3. By way of example, a film comprising the principal GMR structure function has an Fe pin layer 301, Cu spacer layer 302, and IrMn free layer 303. The direction of magnetization of the pin layer 301, which is magnetized in advance in a constant direction 304, is unaltered by the external magnetic field 305. On the other hand, the direction of magnetization 306 of the free layer 303 can be reversed by the external magnetic field 305. In multiple-layer films, the electrical resistance value when the pin layer 301 and the direction of magnetization of the free layer 303 are opposed, as in FIG. 3(b), is different than when they are the same, as in FIG. 3(a). Accordingly, when a voltage is imparted into the multiple-layer film MR, such as shown in FIG. 4, the magnetic data can be detected by the measurement of the resistance values.
Utilizing the anisotropy of the electric resistance, the leakage magnetic field of a magnetic disk is detected and can be used in heads of magnetic disks. In addition, electrical resistance changes are maintained even if there is no electric current flow, so their application as a non-volatile memory (MRAM: Magnetic Random Access Memory) is anticipated.
In reality, these GMR structures are laminated multiple-layer structures of 5 to 9 layers of magnetic and non-magnetic materials and, in the production thereof, by virtue of the fact that the film is grown while a magnetic field is imparted, the pin layer, which is supported in the direction of magnetization, must be magnetized in the one direction.
As is shown in FIG. 5, for the final formation of elements, patterning must be performed with pellets 503 of the MR multi-layer structure aligned with a prescribed direction 502 of the substrate 501. In order to afford the uniformity of the characteristics of these elements within the substrate surface, a magnetic field 504, applied to the elements during growth, must conform with the prescribed direction of the substrate and be imparted uniformly within the substrate surface.
Hitherto, a substrate of diameter 100 mm or 125 mm has been employed for the production of magnetic heads and, as shown in FIG. 6, a magnet has been deployed in the outer circumference of the substrate in such a way that a magnetic field of a prescribed direction parallel with the substrate surface is generated and the film is grown. That is to say, a magnet 603, in which a permanent magnet is assembled, is arranged in the outer circumference of a substrate holder 601 and a substrate 602, and a magnetic field vector 604 is imparted in a constant direction on the substrate surface. The numbers in FIG. 6(b) represent magnetic field strength.
In the case of a magnetic film for MRAM or magnetic heads, a magnetic field of uniform direction must be maintained at all times during growth at xc2x11.5 degree or less from the prescribed orientation and, if a displacement greater than this occurs, large deviations in the pin layer holding power arise, and a nonuniformity in product performance occurs which markedly lowers the productivity.
On the other hand, because the characteristics of a magnetic device are altered significantly depending on the film thickness, uniformity of film thickness within the substrate surface is extremely important. This is explained with reference to FIG. 7. FIG. 7(a) is a specific example of an MR structure, in which the pin layer is a 2-layer configuration of CoFe 701 and NiFe 702. FIG. 7(b) shows, taking the film thickness of the CoFe layer 701 as 8 nm, the changes in holding power when the film thickness of the NiFe layer 702 was altered from 0.2 to 20 nm. As is shown in the diagram, it can be seen that the holding power was significantly altered even when the film thickness of the NiFe layer was different by just 1 nm. For this reason, when the uniformity of film thickness within the surface is poor, large deviations are generated in the holding power of devices taken from the substrate and the yield is markedly lowered. In this way, the uniformity of film thickness is extremely important in terms of consideration of productivity, and the film thickness distribution within the substrate surface [=(Maximum valuexe2x88x92Minimum value)/(Maximum value+Minimum value)] must be xc2x11.5% or less and, in estimates of the performance of devices of the prior art, it must be suppressed to xc2x11% or less.
To improve the uniformity of film thickness within the substrate surface, a method exists in which the center axis of an evaporating source is arranged to be offset from the substrate central axis, and the film is grown while the substrate is rotated. This is a method hitherto employed in sputtering methods, vacuum-deposition methods, and MBE (Molecular Beam Epitaxy) (J. Sakai, S. Murakami, et al., J. Vacuum Science and Technology B 1989 p 1657). An example of a configuration of a sputtering device of the prior art employed for the growth of a MR film is shown in FIG. 8.
FIG. 8(a) is a diagram that shows the geometrical position relationship between a substrate 801 and a sputtering target 804. The sputtering target 804, is offset 805 in the outer circumferential direction from a substrate center axis 802, and is fixed at a diagonal angle 806. During film manufacture, the substrate 801 has self-rotation 803 about the substrate center axis 802. FIG. 8(b) shows the film thickness distribution when a film is formed on a substrate of diameter 200 mm using a target of diameter 87.5 mm. The film thickness distribution using a substrate of diameter 200 mm [=(Maximum valuexe2x88x92Minimum value)/(Maximum value+Minimum value)] is xc2x10.45% and, by the employment of an offset-growth methodxe2x80x94which involves substrate rotationxe2x80x94an extremely good film thickness uniformity can be obtained even if a comparatively small evaporating source is employed.
It will be noted that, to obtain a good film thickness distribution within the surface without the use of substrate rotation, by way of example, for a substrate of 200 mm a large sputtering target of diameter 450 mm or more is required, and the device costs and material cost are very high. In addition, in the case in which a different type of material is continuously grown while maintaining in vacuum without contaminated gas, a large chamber in which a plurality of large targets are arranged is required and extremely unfavorable conditions, from the point of view of economics, have to be accepted.
Accordingly, using a device in which a large substrate of diameter 125 mm is to be processed, a configuration is adopted in which the substrate is arranged in the approximate center of the chamber, the target center axis is displaced outward from the substrate center axis, and the substrate caused to rotate and, by virtue of this, it is possible for a film thickness distribution within the substrate surface of xc2x11% or less to be achieved with a comparatively small chamber and a small sputtering target.
Based on the device configuration noted above, by way of example, a device for forming the above-noted GMR structure pin layer is shown in FIG. 2. FIG. 2 is a type cross-sectional diagram that shows a sputtering device for obtaining a uniform magnetic field and good surface film thickness uniformity.
The sputtering device is configured from a stainless steel vacuum chamber 101, in which a target and substrate holder are arranged in the inner part, an exhaust system 102, and a gas supply system 103. In the upper part of the vacuum chamber 101, a substrate holder 105 and magnet 106 are fixed to a support stand 125, and the support stand 125 is linked with a motor 124 by way of a rotating shaft 126. Accordingly, the substrate can be rotated while the orientation of the substrate mounted on the substrate holder relative to the orientation of the parallel magnetic field due to the magnet is maintained constant at all times. It will be noted that, a magnetic fluid seal 110 is employed for the sealing of the rotating shaft. A lift pin 107, which is provided so as to pass through the rotating shaft 126 and the substrate holder 105, is moved vertically by a cylinder 109 when the substrate is carried in and out, and the transfer of the substrate is performed between a robot (not shown in the diagram) and the substrate holder 105. It will be noted that, in the lower end part of the lift pin 107, a bellows 108 is deployed.
On the other hand, the center axis of a target 115, in the upper part of the chamber, is offset from the center axis of the substrate.
A description will be given of the steps for film formation within a magnetic field in which the sputtering device of FIG. 2 is employed.
The chamber 101 is exhausted to a pressure of 5xc3x9710xe2x88x927 Pa with a Cryo-pump 102, and the rotation shaft 126, when the substrate is transferred from the robot and mounted on the substrate holder 105, is stopped at a position established in advance in such a way that the prescribed direction of the substrate and the direction of the magnetic field are aligned.
The prescribed orientation of the substrate is turned in a load-lock chamber (not shown in the diagram) to be transferred to the robot (not shown in the diagram), and is mounted on the lift pin 107 through a port 104. The lift pin 107 is lowered to mount the substrate 120 on the substrate holder 105. At this time, the direction of the magnetic field due to the magnet 106 and the prescribed direction of the substrate are aligned.
The rotation of the substrate 120, together with the substrate holder 105 and magnet 106, is initiated by the by a rotation motor 124, and this reaches the prescribed rate of rotation of 36 rpm after 150 seconds.
Next, a valve 118 is opened and an Ar gas of a flow amount controlled by a flow meter, not shown in the diagram, is introduced. A DC voltage from a DC power source (not shown in the diagram) is imparted to a sputtering target 115 and the Ar gas is excited to generate plasma. After a few seconds, when the plasma has stabilized, a shutter 116 is opened by a shutter drive mechanism 117, and the growth of film on the substrate is initiated. The shutter 116 is closed using time control and the growth is stopped. DC voltage to the target is interrupted and, simultaneously, electric current to the rotation motor 124 is interrupted. The rate of rotation of the substrate 120 is gradually lowered and, after approximately 150 seconds, the rotation of the substrate 120 is stopped. At this time, using a sensor or the like fixed to the substrate rotating mechanism, the substrate is turned to a prescribed orientation and stopped.
The lift pin 107 is raised and the substrate recovered by the robot. Then an unprocessed substrate is mounted on the lift pin and the same process is repeated.
As is described above, the substrate is arranged to conform with the orientation of the magnet within a range of xc2x11.5 or less, and the substrate and magnet must be synchronized and rotated at a rate of rotation of, at least 30 rpm, and normally 36 rpm. However, by way of example, even in the case of a magnet which generates, in a substrate diameter of 200 mm, a parallel magnetic field of minimum magnetic field strength 0.064 A/m (500e), and is formed in a ring-shape by a method in which powerful permanent magnetsxe2x80x94presently marketedxe2x80x94pull against each other, the magnitude thereof is one of, at the least, an inner diameter of 430 mm, outer diameter of 480 mm and height of 40 mm, and the weight thereof reaches 18 kg.
For this reason, in the configuration of the device of the prior art shown in FIG. 2, a magnet of external diameter 480 mm, weight 18 kg and inertial momentum 3.8 kg m2 must be stopped and rotated for each processed substrate. It takes 150 seconds, which constitutes a long time, from stoppage until steady rotation, and this factor hinders improvements to productivity. In addition, there are problems in that a heavy load is placed on the bearings and the like of the rotation shaft at each rotation and stoppage of said magnet, and the device life span and accompanying maintenance cycle are short.
An objective of the present invention, which resolves the above-noted problems of the prior art, is to provide, in a substrate processing device and substrate processing method in which growth of a film is continuously performed by rotation of a substrate while imparting a magnetic field in a prescribed direction of the substrate, a substrate processing device and substrate processing method in which, even using a large substrate, by way of example 150 mm, the time taken to reach steady rotation of the substrate is shortened, productivity is improved, and a longer life span is achieved.
In a substrate processing device of the present invention, a film is grown on a substrate while a magnetic field, by a magnet arranged in the periphery of a substrate holder, is imparted on to the surface of a substrate mounted on said substrate holder while said substrate holder is rotated. A rotation mechanism for the abovementioned magnet and a rotation mechanism for the abovementioned substrate holder are independently provided. Furthermore, the substrate processing device is provided with a means for detection of the abovementioned magnetic field orientation, a means for detection of the prescribed orientation of the abovementioned substrate, and a mechanism which, using the output of the two detection means, affords rotation in which the prescribed direction of the abovementioned substrate and the direction of the abovementioned magnetic field are aligned within a prescribed angle.
In one embodiment of the present invention, encoders are provided in the rotation mechanism of the abovementioned magnet and in the rotation mechanism of the abovementioned substrate holder and are employed as a means for detection of the direction of the abovementioned magnetic field and a means for detection of the prescribed direction of the abovementioned substrate. When rotation is performed with the prescribed direction of the abovementioned substrate and the direction of the abovementioned magnetic field aligned within a prescribed angle, a mechanism is activated to bring the rotation parts of the abovementioned magnet and the abovementioned substrate holder into proximity and contact with each other. And, a mechanism in which at least one pair of protruding members attached to said rotations parts are brought into contact in the direction of rotation.
In this way, a configuration is adopted in which a rotation mechanism for the magnet and substrate holder are independently provided and independently controlled, and the magnet, which is large and heavy and has a large inertial momentum, is rotated at all times at a prescribed rate of rotation and, when the substrate is to be exchanged, only the substrate holder, which is light and has a small inertial momentum, is stopped and rotated. Thus, the time taken to reach stoppage and to reach a steady rotation of the substrate can be markedly shortened. As a result, it is possible for the time required for exchange of the substrate to be shortened and for the throughput of the device to be significantly improved.
Furthermore, because the substrate holder is light in weight, there is almost no burden placed on the bearings and the like during rotation and the life span of the device is extended.
Furthermore, in one embodiment of the present invention, the substrate holder is caused to be rotated by an induction magnetic field generated by the rotation of the abovementioned magnet. When the substrate holder is configured using a conducting material such as aluminium, because the substrate holder is automatically rotated due to the effect of the induction magnetic field generated by the rotation of the magnet, the motor and the like used for substrate rotation can be omitted, and a simplification of the configuration of the device is possible. In addition, it is preferable that at least one coil, vertical with respect to the substrate surface, be arranged in the outer circumferential surface part of the abovementioned substrate holder and, by virtue of this, an even larger induction magnetic field is obtained and the time taken to reach a steady rotation of the substrate holder can be shortened.
In a substrate processing method of the present invention, a film is grown on a substrate while a magnetic field, by a magnet arranged in the periphery of a substrate holder, is imparted on to the surface of a substrate mounted on said substrate holder while said substrate holder is rotated. The abovementioned magnet is continuously maintained in the rotation state at all times and, when the substrate is to be exchanged, exchange of the substrate is performed with only the rotation of the abovementioned substrate holder stopped. When the abovementioned substrate holder is rotated again and the direction of the abovementioned magnetic field and the prescribed direction of the abovementioned substrate are within a prescribed angle, rotation parts of the abovementioned magnet and the abovementioned substrate holder are brought into contact with each other to afford integral rotation of the abovementioned magnet and substrate holder, following which the growth of the film is performed.
In addition, in one embodiment of the present invention, the abovementioned substrate holder is caused to be rotated by an induction magnetic field generated by the rotation of the abovementioned magnet.